1. Field of the Invention
My invention relates to sound reproducing apparatus, and in particular to an improved vibration transmission mechanism for a phonograph of the type wherein the mechanical vibrations set up in a reproducing stylus by the undulations of a record groove are transmitted directly (i.e., without the process of electrical amplification) to a speaker diaphragm, causing same to generate audible vibrations of the air.
2. Description of the Prior Art
There has been known and used a phonographic vibration transmission mechanism comprising a vibration transmission rod which is maintained in relative sliding contact with a tone arm carrying a stylus and which is further urged against, or rests upon, a speaker or its armature. The vibration transmission mechanism of this type, as heretofore constructed, has been subject to the drawback that the volume of sound generated by the speaker unnecessarily changes to an appreciable degree in the course of playback.
I have found that the above drawback is caused by the change, with the progress of playback, in the distance between the stylus on the tone arm and the variable point of contact of the latter with the vibration transmitter rod and in the distance between this variable point and the fixed point of contact of the vibration transmitter rod with the speaker. No particular attention has so far been paid to such changes in the effective lengths of the vibration transmitting members.
According to my Japanese Patent Application No. 46-31762, for example, the distance between the stylus and the variable point of contact between tone arm and vibration transmitter rod is maximum when the tone arm is in its starting position at the perimeter of the disc record, gradually diminishes to a minimum in the middle of playback, and again increases toward the end of playback. Since the tone arm is usually molded of plastics, which is comparatively easy to absorb vibrations, the sound-producing vibrations transmitted therethrough from the stylus to the vibration transmitter rod are of minimum intensity or amplitude at the start and the end of playback and are of maximum intensity in the middle of playback.
The vibration transmitter rod, on the other hand, is usually made of material which is considerably less easy to absorb vibrations than plastics. Hence, the greater the distance between its variable point of contact with the tone arm and its fixed point of contact with the speaker, the more does the vibration transmitter rod amplify the vibrations before they reach the speaker. Since this distance also changes with the progress of playback, however, the amplitude of the sound-producing vibrations transmitted from the stylus to the speaker is dually affected by the varying distance between the stylus and the point of contact of the tone arm with the vibration transmitter rod and by the varying distance between that point and the point of contact of the rod with the speaker, resulting in the aforesaid unnecessary changes in sound volume in the course of playback.